1. Field of the Invention
The present invention relates to broadband signal switching equipment and more particularly to cross point matrices constructed in field effect transistor technology.
2. Description of the Prior Art
If emitter-coupled logic (ECL) technology can be characterized by properties such as high working speed, moderately high degree of integration and moderately high dissipated power, then field effect transistor (FET) technology, given only moderate working speeds in comparison thereto, however, is distinguished by an extremely high degree of integration and by extremely low dissipated powers. These latter properties lead to efforts to penetrate into speed regions previously reserved for the bipolar technique with integrated circuits in FET technology.
Known in this context, from EP-A-O No. 264 046, is a broadband signal switching equipment comprising a crosspoint matrix that comprises matrix input lines respectively formed with two signal conductors which, first of all, are respectively connected to two differential (complementary) outputs of an input digital signal circuit and, secondly, can be connected via crosspoints to matrix output lines that likewise are respectively formed with two signal conductors. These matrix output lines have their two signal conductors respectively connected to the two signal inputs of an output amplifier circuit formed with a differential amplifier. A crosspoint matrix constructed in FET technology therefore has pairs of switching elements provided in the crosspoints and respectively formed of two switching transistors respectively charged with a through-connect signal or, respectively, inhibit signal at the control electrode. The switching transistors of these pairs of crosspoint switches respectively have a main electrode connected to the one or, respectively, other signal conductor of the appertaining matrix output line that is, in turn, provided with an output differential amplifier having a trigger behavior, whereby the pairs of crosspoint switches each respectively comprise two series transistors. The two series transistors respectively form a series circuit with a switching transistor, the series transistors respectively having their control electrode connected to the one or, respectively, to the other signal conductor of the appertaining matrix input line and having their respective main electrode that faces away from the series circuit connected via a sampling transistor to the one terminals (ground) of the operating voltage source to whose other terminal every signal conductor of the respective matrix output line is connected via a series transistor. The series transistors and the sampling transistor have their control electrodes respectively charged oppositely one another with a switching matrix network drive clock that divides a bit through-connect time interval into a precharging phase and into the actual through-connect phase, so that both signal conductors of the matrix output lines are charged via the respective precharging transistor at least approximately to the potential prevailing at the other terminal of the operating voltage source in every pre-phase given an inhibited sampling transistor.
In addition to the advantages that are connected with a crosspoint matrix constructed in FET technology, this known broadband signal switching equipment provides the further advantage that, first of all, given an inhibited crosspoint, no disturbing signals can proceed via the crosspoint to the matrix output, even without additional attenuating measures and that, secondly, and given a conductive crosspoint, charge reversals of the matrix output lines potentially occurring in the actual bit through-connection always proceed in only one charge-reversal direction from the one operating potential corresponding to the one signal state and, therefore, and unequivocal transition of the through-connected digital signal appearing at the output of the switching equipment from the one and the other signal state is already established with a small charge reversal (corresponding to the transgression of a threshold adjacent to this value of operating potential and corresponding to the break over point of the differential amplifier) and, therefore, correspondingly fast.